Heat resisting corrosion resisting iron chromium alloy

ABSTRACT

A HEAT RESISTING CORROSION RESISTING ALLOY OF FE, CR, AL, AND Y, CHARACTERIZED BY FURTHER CONSTITUENTS THEREOF, GD AND/OR DY. 10 TO 40 PARTS BY WEIGHT OF GD AND/OR DY ARE MIXED WITH 100 PARTS BY WEIGHT OF Y. THIS ALLOY IS USEFUL AT 1350*C., HIGHLY CORROSION RESISTING, HIGHLY WORKABLE, AND HAS A HIGH TENSILE STRENGTH AT AN ELEVATED TEMPERATURE.

United States Patent US. Cl. 75-124 2 Claims ABSTRACT OF THE DISCLOSURE A heat resisting corrosion resisting alloy of Fe, Cr, Al, and Y, characterized by further constituents thereof, Gd and/or Dy. to 40 parts by weight of Gd and/or Dy are mixed with 100 parts by weight of Y. This alloy is useful at 1350 0., highly corrosion resisting, highly workable, and has a high tensile strength at an elevated temperature.

BACKGROUND OF THE INVENTION Field of the invention The field of art to which this invention pertains is metallurgy. This invention would be classified into Class 75, Subclass 1 in the U3. Patent Classification.

Description of the prior art It has been Well known that the alloys of Fe-Cr-Al series are highly heat resisting and highly corrosion resisting. Many proposals in connection with practical uses thereof have been published. However, high heat resistance is incompatible with workability in each of these alloys, or these highly heat resisting alloys are generally highly brittle.

One object of this invention is to provide an alloy which may be useful at a temperature of as high as 1350 C. in air.

Another object of this invention is to provide an alloy which is highly corrosion resisting in the combustion gas, in nitrogen, and in vacuo.

Still another object of this invention is to provide an alloy which is low brittle and has a fair workability.

Further another object of this invention is to provide an alloy which has a high tensile strength at an elevated temperature.

SUMMARY OF THE INVENTION Briefly stated in accordance with one aspect of this invention, there is provided an alloy comprising from 15.1 to 19.9 percent by weight of chromium, from 0.5 to 6.0 percent by weight of aluminum, from 0.01 to 1.5 percent by weight of yttrium, from 0.001 to 0.6 percent by weight of gadolinium or dysprosium or a mixture of the two, and the balance of iron.

The range of chromium to be contained in this alloy is defined from 15.1 percent to 19.9 percent by weight on the ground that more than 20 percent of chromium deteriorates workability of the alloy while less than percent of chromium deteriorates corrosion resistance remarkably. The range of aluminum to be contained in this a1- loy is defined from 0.5 percent to 6.0 percent by weight on the ground that less than 0.5 percent of aluminum deteriorates corrosion resistance remarkably while more than 6.0 percent of aluminum deteriorates workability. The range of yttrium to be contained in this alloy is defined from 0.01 percent to 1.5 percent by weight on the ground that less than 0.01 percent of yttrium deteriorates corrosion resistance of the alloy while more than 1.5 percent of yttrium deteriorates workability of the alloy. The range of gadolinium and/or dysprosium to be contained in this alloy is defined from 0.001 percent to 0.6 percent by ice weight. It is more pertinent to define the content of either of gadolinium, dysprosium, or a mixture of the two in relation with the content of yttrium. That is, from 10 parts by weight to 40 parts by weight of the two elements, solely or as a mixture, are to be accompanied by every parts by weight of yttrium in this alloy. If either one or both of the two is contained less than 0.001 percent by weight in this alloy, the effect of yttrium contained in the alloy is not advantageously afiected. On the other hand, if either one or both of the two is contained more than 0.6 percent by weight in this alloy, the workability of the alloy is deteriorated.

By virtue of Gd and/0r Dy contained in the alloy in accordance with this invention, corrosion resistance of the alloy is improved and at the same time workability thereof at the normal temperature is remarkably advanced. Gd and/or Dy contained in the alloy :in accordance with this invention contribute to improvement in its tensile strength at an elevated temperature remarkably. It is considered that these advantageous inffuences of Gd and/or Dy contained in this alloy in accordance with this invention, which necessarily contains Y, are resulted from coexistence of Gd and/or Dy with Y, because these three elements are very approximate in ionic radius one after another. Thus ionic radii of Y, Dy and Gd are 1.08 A., 1.07 A., and 1.11 A., respectively. In case where a compound is formed, for example, Al-Y-Cr are oxidized, on the surface of the alloy in accordance with this invention at an elevated temperature, it is considered that, by virtue of mutual catalytic action of the Gd and/or Dy with Y, a strong stable oxide is formed at an early period and be comes ceramic. It is considered that this mutual catalytic action is introduced from the approximation in ionic radius and that the improvement in properties of the alloy in accordance with this invention at an elevated temperature is derived from the ceramic substance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The essential features of the invention are illustrated by the following examples although it is not intended to limit the invention specifically thereto.

Example 1.Raw materials consisting of pure iron, extra low carbon ferrochrome, highly pure aluminum, yttrium metal, gadolinium metal, and gysprosium metal were molten together in vacuo in a high frequency furnace (l0 kva.) and cast into an ingot, of which weight was 3 kg., diameter was 30 mm, and composition was 18 parts of Cr, 4 parts of A1, 0.3 part of Y, 0.05 part of Gd, 0.05 part of Dy, and balance of Fe, by weight. Thus the weight of Gd plus weight of lDy were 0.1 while the weight of Y was 0.3, so that the 0.1 of the weight of Gd plus Dy lay within the range of from 10 to 40 per 100 of Y.

The ingot was machined for removing the surface and forged into a billet of 16 mm. in diameter at a temperature of 1200 C. The billet was rolled into a wire rod of 7 mm. in diameter at a temperature of 1100 C. The wire rod was subjected to heat treatment and then cold-drawn into a wire of 0.5 mm. in diameter through dies.

Example 2.-A wire of 0.5 mm. in diameter, of which composition was 18 parts of Cr, 4 parts of A1, 0.3 part of Y, 0.1 part of Gd, and balance of Fe, by weight, was produced similarly to the preceding example exclusive of Dy.

Example 3.-A wire of 0.5 mm. in diameter, of which composition was 18 parts of Cr, 4 parts of A1, 0.3 part of Y, 0.1 part of Dy, and balance of Fe, by weight, was produced similarly to the Example 1 exclusive of Gd.

Example 4.-The wires produced in the Examples 1, 2 and 3 were tested together with three contrast test pieces in connection with life. The three contrast test pieces were similar wires produced similarly to the Examples 1, 2

and 3 and of which composition were (A) 25 parts of Cr, 4 parts of Al, and balance of Fe, (B) 25 parts of Cr, 4 parts of A1, 1 part of Y, and balance of Fe, and (C) 18 parts of Cr, 4 parts of A1, 0.3 part of Y, and balance of Fe, respectively. The life test was done in accordance with the procedure and by employing a life testing apparatus defined by the Japanese Industrial Standards, in which each test piece is repeatedly and cyclically heated up to a temperature of 1300 C. in air for two minutes and left to be cooled by deenergizing the heat source for another two minutes. This heat treatment is repeated cyclically until the test piece is burnt out in the testing apparatus, which is classified into the U type and the I type. The life value of the test piece is defined as the number of repetition of the heat treatment.

By testing the three test pieces of the alloys in accordance with this invention and the three contrast test pieces, the following results were yielded:

TABLE 1.LIFE TEST (IN U TYPE) Example 5.-SOIne other properties were tested with the test pieces produced in the Examples 1, 2 and 3 together with the pieces for the contrast test as used in the preceding test, yielding the following results:

TABLE 2.TENSILE STRENGTH AND OXIDATION Weight increased by oxidation in Tensile strength (kg/mm!) air at 1,300 O. for 100 hrs., At 1,200 C. At 25 0. percent It is to be understood that the alloy in accordance with this invention has an excellent workability and a superior tensile strength at an elevated temperature, shown as the test pieces of the Examples 1, 2 and 3, comparing with conventional contrast test pieces (A), (B) and (C).

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A heat resisting corrosion resisting alloy consisting essentially of from 15.1 to 19.9 percent by weight of chromium,

from 0.5 to 6.0 percent by weight of aluminum,

from 0.01 to 1.5 percent by weight of yttrium,

from 0.001 to 0.6 percent by weight of at least a member selected from the group consisting of gadolinium and dysprosium and balance iron.

2. A heat resisting corrosion resisting alloy as claimed in claim 1, consisting essentially of from 15.1 to 19.9 percent by weight of chromium,

from 0.5 to 6.0 percent by weight of aluminum,

from 0.01 to 1.5 percent by weight of yttrium,

at least a member selected from the group consisting of gadolinium and dysprosium, total weight of said gadolinium and said dysprosium being from 10 percent to 40 percent of weight of said yttrium, and balance iron.

References Cited UNITED STATES PATENTS 2,190,486 2/1940 Schafmeister -123E 3,017,265 1/1962 McGurty 75126G 3,031,297 4/1962 Baranow 75126G 3,113,991 12/1963 Kleber 75-1266 3,298,826 1/1967 Wukusick 75126G HYLAND BIZOT, Primary Examiner US. Cl. X.R. 

